Liquid-solids circulating fluidized bed

ABSTRACT

A continuous Liquid-Solids Circulating Fluidized Bed (LSCFB) preferably for use as an ion exchanger consists of two fluidized bed columns, a fluidized bed adsorber (downer) operating in conventional fluidized bed mode for adsorption of ions of interest and a fluidized bed riser for desorption of ions (operating as a riser fluidized bed) to provide regenerated particles. Ion exchange particles circulate continuously between the riser and the downer i.e. the particles that have adsorbed ions in the absorber pass from the adsorber (downer) to the desorber where they are regenerated and the so regenerated particles are return to the adsorber near the top of the adsorber column. The LSCFB can be used in processes for continuous recovery of the ions of interest.

FIELD OF THE INVENTION

The present invention relates to a fluidized bed, more specifically, aliquid-solids circulating fluidized bed arrangement specially suited forion exchange processes.

BACKGROUND TO THE INVENTION

Fluidized beds have been used for a number of different applicationssuch as a gas-liquid, gas-liquid-solid contactors and to carry out avariety of different processes such as chemical reactions.

Fluidized beds have found application in ion exchange process. Forexample Chase, H. A., “Purification of Proteins by AdsorptionChromatography in Expended Beds”, TIBTECH 12, 296-303 (1994) describes abatch ion exchange process using a conventional fluidized bed forrecovering proteins from whole fermentation broth with the presence ofbacterial cells. It eliminates the difficult solids separation step andrecovers the desired products directly from unclarified whole broth.This process is a batch process employing a conventional fluidized bed.

Burns, M. A. and D. J. Graves, “Continuous Affinity Chromatography Usinga Magnetically Stabilized Fluidized Bed”, Biotechnology Progress 1,95-103 (1995) suggested a two-column magnetically stabilized fluidizedbed system for the continuous chromatography of biochemical products.The magnetically stabilized fluidized bed system is considered to becomplicated and costly.

Gordon, N. F., H. Tsujimura and C. L. Cooney, “Optimization andSimulation of Continuous Affinity Recycle Extraction”, Bioseparation 1,9-12 (1990) describes a process using mixed reactors as opposed tofluidized bed and reported the continuous affinity recycle extraction ofproteins using well-mixed reactors. This system, although simple andeasy to control, has the disadvantage of a stirred tank system—the ionexchange efficiency is low and large processing volumes are essentialfor even a moderate throughput requirement

Porter and Robert, U.S. Pat. No. 3,879,287, “Continuous ion exchangeprocess and apparatus” (1975) relates to an apparatus for continuous ionexchange. However, the process described is a semi-continuous process asthe recommended eluting means is a batch wise conventional fixed bed ionexchange process.

Himsley and Alexander, U.S. Pat. No. 4,279,755: Continuouscountercurrent ion exchange process (1993) teaches a continuouscountercurrent ion exchange process for absorbing ions of interest ontoion exchange particles from a feed liquor containing ions which whenabsorbed on the particles cause the density of the particles toincrease. The process comprises the steps of (1) flowing the feed liquorupwardly through a main bed of ion exchange resin particles contained ina main chamber of an absorption column and thereby maintaining the bedin fluidized state; (2) continuously collecting the denser loadedparticles from the lower region of the absorption column; (3) passing anoutflow of the feed liquor from the upper region of the main chamberupwardly into the lower region of the polishing chamber containing asecondary bed of fluidized ion exchange resin particles whereby residualions of interest are polished from the liquor, and (4) producing abarren liquor flowing out of the upper region of the polishing chamber.Again, this is a semi-continuous process as the stripping and theregeneration of the loaded ion exchange particles cannot be performed inthis device.

BRIEF DESCRIPTION OF THE PRESENT INVENTION

It is an object of the present invention to provide a circulatingfluidized bed system for liquid solids contact and interaction, morespecifically a Liquid-Solids Circulating Fluidized Bed (LSCFB) ionexchanger.

It is also an object of the present invention to provide a process forcontinuous recovery of the ions of interest for example contaminants inliquid streams or value added products from waste steam using aLiquid-Solids Circulating Fluidized Bed (LSCFB) ion Exchange system.

Broadly the present invention relates to a fluidized bed systemcomprising a first fluidized bed, means to feed solids into said firstfluidized bed adjacent to a first end of said first fluidized bed andmeans to feed a first fluid into said first fluidized bed adjacent to asecond end of said first fluidized bed, said second end being remotefrom said first end so that said solids and said first fluid flow incounter current, a second fluidized bed, said second fluidized bed beingan entraining fluidized bed wherein a means for introducing solids and ameans for introducing a second fluid into said second bed are bothadjacent to the one end of said second fluidized bed so that said solidsand said second fluid introduced into said second bed flow concurrentlythrough said second bed from said one end toward another end of saidsecond fluidized bed remote from said one end, first means connectingsaid first fluidized bed to said second fluidized bed adjacent to saidsecond end of said first fluidized bed and said one end of said secondfluidized bed and said first means connecting including said means tofeed solids into said second fluidized bed, and second means connectingsaid first and said second fluidized beds adjacent said first end ofsaid first bed and said other end of said second fluidized bed, and saidsecond means connecting including said means to feed solids into saidfirst fluidized bed.

Preferably said first and second fluidized beds are substantiallyvertical columns. Preferably said second means connecting said first andsaid second fluidized beds includes a separator means for separatingsolids from fluid and exhausting such separated fluid to provideseparated solids.

Preferably second means connecting said first and said second fluidizedbeds further includes a washer for washing said solids before they arefeed into said first end of said first fluidized bed.

Preferably said first means connecting said first and said secondfluidized beds includes a second washer washing solids adjacent to saidsecond end of said first fluidized bed before they are introduced intosaid second fluidized bed.

Preferably said first fluidized bed is an absorber for separating ionicproducts of interest and said second fluidized bed is a desorber fordesorption of ionic products and said solids are ion exchange particles.That is, the said liquid-solid circulating fluidized bed system canpreferably be used to recover ionic products of interest by passing ionexchange particles in countercurrent flow with a feed stream of a firstfluid through a first fluidized bed for adsorption of ionic products ofinterest from said feed stream of said first fluid, transferring saidparticles with adsorbed ionic products of interest from said firstfluidized bed to a second fluidized bed and passing said ion exchangeparticles with absorbed ionic products in countercurrent flow with anextract buffer of a second fluid through said second fluidized bed fordesorption of said adsorbed ionic products of interest, separating saidsecond fluid containing said ionic products of interest desorbed fromsaid ion exchange particles by said second fluid to provide regeneratedion exchange particles and returning said regenerated ion exchangedparticles into said first fluidized bed to flow in countercurrent withsaid first fluid.

Preferably said ion exchange particles with absorbed ionic products arewashed before being introduced into said second fluidized bed.

Preferably said regenerated ion exchange particles are washed beforebeing returned to said first fluidized bed

Preferably said ionic product is a protein and said first fluid is afermentation broth.

Preferably said ionic product is a metal and said first fluid isseawater.

Preferably said ionic product is an enzyme and said first fluid isdextrose syrup.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, objects and advantages will be evident from thefollowing detailed description of the preferred embodiments of thepresent invention taken in conjunction with the accompanying drawings inwhich;

FIG. 1 is a schematic illustration of the method and apparatus of thepresent invention

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 the present invention is composed of a pair offluidized beds a first fluidized bed 10 and a second fluidized bed 12interconnected at their adjacent ends by solid transfer and washingsystems generally indicated at 14 and 16 respectively. The firstfluidized bed 10 is a conventional counter-current flow bed whereinsolids (solid particles such as ion exchange beads) as indicated at 18enter adjacent to the top of the bed 10 as indicated by the line 17 andflow downward and a first fluidizing fluid namely the feed liquor 20enters the bed 10 as indicated schematically at 22 at the lower end 24of the bed 10 and flows upward in counter current with the particles 18.

The second fluidized bed 12 on the other hand is a riser fluidized bedwherein the solid particles 18 transferred from bed 10 via transfersystem 14 enter the bed 12 adjacent to the lower end 26 of the bed 12and flow upward in co-current relation with a second fluidizing fluid 28(such as extract buffer) which enters the bed 12 under pressure in theillustrated arrangement via nozzle 30 and inlet 32 both adjacent to thelower end 26 of the bed 12 and flows upward through the bed 12 carryingthe particles 18 in its flow.

The distributor of the second fluidized bed 12 divides the incomingstream of extracting buffer 28 into two sub-streams: the primary 60 andthe auxiliary 62 streams. The primary stream 60 is introduced throughnozzle 30 which projects into the second fluidized bed column 12. Thisdesign increased the pressure drop across the bottom solids return pipe42 and makes the system more stable. The auxiliary stream 62 isintroduced into the bottom 26 of the second fluidized bed 12 through aperforated plate inlet 32. The function of the auxiliary stream 62 is tostir up the particles at the bottom of the second fluidized bed 12 to beentrained up the second fluidized bed by the combination of the primaryand auxiliary liquid streams 60 and 62. The two streams 60 and 62 mayalso be combined into a single stream and the fed through a singledistributor at the second fluidized bed 12 bottom end 26.

As above indicated the solid particles 18 enter at inlet 17 and traveldownward through the bed 10. After they have traversed the fluidized bed10 the particles 18 enter into the transfer system 14 which includes awashing stage 34 in a conical or funnel shaped bottom end 35 of thehousing containing the bed 10 and into which wash water from a source isinjected via nozzle 38 positioned adjacent to the apex of the cone inthe bottom outlet 40 of the bed 10. The injected wash water 36 travelsin counter current to and washes the particles 18 when they leave thefluidized bed 10. The wash water dilutes the feed stream and exits fromthe top of bed 10 through outlet 44. The washed particles 18 then passvia transfer pipe 42 and are introduced into the second fluidized bed12.

The function of the wash section 34 is to rinse the loaded particles 18and to prevent the feed stream 20 from being carried to the secondfluidized bed 12 by the particles 18. The bottom solids return pipe 42is located below the wash section 34. It connects the bottoms of thefirst fluidized bed 10 and the second fluidized bed 12. Duringoperations, loaded ion exchange particles are transported into the baseof the second fluidized bed 12 through the bottom solids return pipe 42to make up the particles 18 entrained up along the second fluidized bed12. The bottom solids return pipe 42 operates as a packed moving bed.This is the most important mechanism for forming the dynamic sealbetween the second fluidized bed 12 and the first fluidized bed 10. Thedynamic seal is critical for the success of this continuous ion exchangeprocess, which employs two liquid streams of different properties.

In the LSCFB ion exchange system of the present invention, the solidscirculation rate is controlled by a butterfly valve schematicallyindicated at 70 located on the bottom solids return pipe 42. Themechanical valve is preferred over a hydraulic valve due to the lowdensity of most ion exchange particles, which makes the operation of thehydraulic valve more difficult. An additional advantage of using themechanical valve in this situation is that it enhances the pressure dropacross the solids return pipe 42 and therefore makes the system morestable. The auxiliary liquid stream 62 may be used to provide additionalcontrol of the solids circulation rat.

The fed liquor 20 as above described enters at the bottom of the bed 10,travels in countercurrent to the particles 18 trough the bed 12 andleaves at the top of the bed as indicated at 44. The fluid exiting from44 is discarded as waste or as a purified stream in the case ofcontaminant removal.

The second fluidizing fluid (extract buffer) 28 and the particles 18from line 42 travel in co-current fashion upward through the bad 12 andare regenerated and then enter the transfer system 16 which includes aseparator such as the fluid vortex type separator 46 having a fluidoutlet 48 through which the second fluidizing fluid 28 is removed and asolids outlet through a wasting stage 50 at the bottom. This fluidexiting from outlet 48 contains the ions of interest and may besubjected to further downstream processing or membrane treatment toconcentrate the ions of interest. Washing fluid is injected via nozzle52 at the bottom of the washing stage 50 and flow upward incountercurrent with the downcoming solids (regenerated solid particles)18 and the so washed particles 18 enter the inlet tube delivering theregenerated particles 18 into the top of the bed 10. The washing fluiddilutes the extract buffer and exits from the outlet 48.

The operation of the invention will be described in relation to ionexchange process, but it may be used in other potential application asdescribed below.

In the process of ion exchange, the feed liquor 20 is introduced viainlet 22 into the bottom (second) end of the first fluidized bed 10(downcomer 10) and the regenerated particles 18 from the bed 12 areintroduced via line 17 adjacent to the first or the top of the firstfluidized bed 10, i.e. the feed 20 and regenerated beads are introducedat opposite ends of the first fluidized bed 10.

The falling particles 18 and the up-flowing feed liquor 20 contactcounter-currently and the target ions in the feed 20 are adsorbed ontothe ion exchange particles 18 in the first fluidized bed 10. Thede-ionized liquor leaves from the top of the first fluidized bed throughthe raffinate outlet 44 and the loaded particles 18 fall into thewashing stage 34 at the base of the first fluidized bed 10 are rinsedand then transferred via line 42 to the base of the second fluidized bed12.

During operations, as above described loaded ion exchange particles aretransported into the base of the second fluidized bed 12 through thebottom solids return pipe 42 to make up the particles 18 entrained upalong the second fluidized bed 12. The bottom solids return pipe 42operates as a packed moving bed forming the dynamic seal between thesecond fluidized bed 12 and the first fluidized bed 10.

The extracting buffer 28 is applied to the second fluidized bed 12 atthe bottom. The superficial liquid velocity in the second fluidized bed12 is maintained in a range higher than the terminal velocity of the ionexchange particles 18 so that the loaded particles are carried upward bythe upflowing buffer 28. The buffer 28 and the loaded ion exchangeparticles 18 hence contact co-currently while desorption andregeneration of the particles 18 proceed in the second fluidized bed 12.The extract 28 and the regenerated ion exchange particles 18 areseparated by a liquid-solids separator 46 adjacent to the top of thesecond fluidized bed 12. The extract is then collected from the extractoutlet 48 and the regenerated ion exchange particles 18 returned to thefirst fluidized bed 10 through the top solids return pipe 17, afterbeing rinsed through the wash section 50.

The liquid-solids separator 46 in the illustrated arrangement is ahydraulic (but can be any other type of separator) cyclone, whichseparates the regenerated particles 18 from the extract 28. The extractoutlet 48 is located on the separator preferably at the same level asthat of the raffinate outlet 44 on the top of the first fluidized bed 10to maintain the pressure balance between the second fluidized bed 12 andthe first fluidized bed 10. To prevent the loss of particles through theextract outlet, a stainless steel mesh (not shown) is preferably used tocover the extract outlet 48.

The top washing section 50 comprises of the funnel bottom of theseparator and return pipe 17. The upward washing water slows down thefalling of the particles 18 and creates a solids layer in the funnelbottom of the separator 46. It also rinses the particles 18 before theirfalling into the top solids return pipe 17 and minimizes theinter-mixing between the extract in the second fluidized bed 12 and thede-ionized liquor at the top of the first fluidized bed 10. The returnpipe 17 (particle inlet to the first fluidized bed 10) enters the firstfluidized bed 10 sufficiently below the outlet 44 to maintain afreeboard section 64 in the upper part of the first fluidized bed 10 ofsufficient height to substantially eliminate carry over of particles 18through the outlet 44.

APPLICATIONS OF THE PRESENT INVENTION

A feed liquor 20 from which ions can be recovered, such as afermentation broth, usually contains a large amount of small solids andrelatively low concentration of desired product(s). Hence, the firsttask in developing a new downstream treatment process usually focuses onthe selection of an appropriate procedure for handling the solidspresent in the feed. This is typically achieved by filtration orcentrifugation. However, the presence of colloidal solids and theviscous properties of many feeds frequently make those methods bothcostly and inefficient. The LSCFB ion exchange system of the presentinvention is an integrated unit operation which can recover desired ionsfrom unclarified whole broth continuously.

The desorption of the target ions and the regeneration of the ionexchange particles are carried out in the second fluidized bed 12. Theloaded ion exchange particles 18 are transported into the base of thesecond fluidized bed 12 through the bottom solids return system 14 andflow co-currently upward with the extracting buffer 28 along the secondfluidized bed 12. The loaded particles are stripped of the target ionsand regenerated in the second fluidized bed 12 before being entrainedinto the liquid-solids separator 46 of the transfer system 16. As thesecond fluidized bed 12 is operated in the circulating fluidizationregime with high liquid velocity, the contact efficiency and the masstransfer rate between the liquid and solids are very high.

In the liquid solids circulating fluidized bed (LSCFB), diagrammed inFIG. 1, the absorption in the first fluidized bed or downcomer 10 andthe desorption in the second fluidized bed or second fluidized bed 12can be carried out in a continuous. The ion exchange particles 18employed in this system should have reasonably large absorption capacityto the target or desired ions and the density of the ion exchangeparticles 18 in the swollen state should be larger than that of the feedliquor. As the first fluidized bed 10 is maintained in the conventionalfluidization regime, the bed voidage could be adjusted to allow thepassage of the particulates in an unclarified feed by controlling thesuperficial liquid velocity in th first fluidized bed. In other words,this system can be used to purify the target ions directly from anunclarified whole broth so that the costly pre-clarification process iseliminated.

In the LSCFB, the adsorption of the target ions are carried out in thefirst fluidized bed 10 and the desorption and the regeneration in thesecond fluidized bed 12. This is a continuous process with the ionexchange particles 18 circulated continuously between the two columns 10and 12. Two different liquid streams, the feed 20 in the first fluidizedbed 10 and the extracting buffer 28 in the second fluidized bed 12, areused in this system. The second fluidized bed 12 is operated in thecirculating fluidization regime and the first fluidized bed in theconventional fluidization regime.

EXAMPLES

In arrangement as shown in FIG. 1, the second fluidized bed 12 is anacrylic column of I.D. 38.1 mm and 3 m in height. The distributor of thesecond fluidized bed 12 divides the incoming stream of extracting bufferinto two substreams: the primary 60 and the auxiliary 62 streams. Theprimary stream 60 is introduced through a stainless steel pipe (I.D. 11mm) (nozzle 30). It project 36 mm into the second fluidized bed column12. Since the liquid velocity in the second fluidized bed is maintainedin a range higher than the terminal velocity of the ion exchangeparicles, the high liquid velocity enhances the contact efficiency andalso the mass transfer rate between the liquid and the particles.

The top washing section 50 as above described comprises of the funnelbottom of the separator 46 and an acrylic pipe of 40 mm in diameter and200 mm in height (pipe 17). The first fluidized bed is a Plexiglascolumn of I.D. 120 mm and 2.5 m in height. The particle entrance 17 onthe first fluidized bed 10 is located 0.813 m below the raffinate outlet44 to prevent the direct loss of particles through the raffinate outlet44. The distributor 22 of the first fluidized bed 10 is a perforatedstainless steel pipe. This distributor allows the particles to fallthrough to the bottom solids return pipe 42 while introducing the feed20 to the first fluidized bed 10.

The bottom washing section 34 is comprised of the funnel bottom of thefirst fluidized bed 10 and a vertical pipe 40 of 40 mm I.D. and 200 mmin height. Wash water is introduced from the base of this column andgoes upward (nozzle 38).

In the LSCFB ion exchange system, the solids circulation rate iscontrolled as above described by a butterfly valve 70 located on thebottom solids return pipe 42.

Table 1 summarizes the experimental result conducted using the apparatusas above described, with whole whey which contains approximately 5.4 g/Lproteins and with an artificial protein solution, the 2 g/L bovinealbumin serum (BSA) solution. The protein recovery from BSA solution wasmuch higher than that from the whey solution. This is because the highionic strength and the fouling effects of the milk-fats in whey solutionreduced the dynamic capacity of the system.

TABLE 1 Summary of parameters of whey protein recovery under differentconditions Protein Protein Feed Protein Conc. Overall Through- Conc.Flow Loading in Raffin- Re- put Feed in Feed rate Rate ate (waste covery(g/hr · Type (g/L) (L/hr) (g/hr) feed (g/L) (%) (kg beads)) Whey 5.4 5.731.2 0.77 78.4 8.2 BSA 2.0 38.4 76.8 0.79 84.0 21.5 Solution

POTENTIAL TECHNOLOGY APPLICATIONS

Potential applications of the invention that the invention is believedto be suitable for include but are not limited to.

a) The recovery of ionic products from biological or non-biologicalfeeds such as protein recovery from fermentation broth, metal recoveryfrom sea water, etc. where suitable ion exchange particles areavailable,

b) The removal of ionic contaminants from products or intermediateproducts, e.g., removal of enzyme from dextrose syrup after theconversion;

c) The desalination of water;

d) Wastewater treatment.

IN SUMMARY Ion Exchange of Target Ions Occurs by:

1. Regenerated ion exchange particles are fed to the first fluidized bedthrough the top solids return pipe; those particles flow down to thelower part of the first fluidized bed to form a particulate bed;

2. The feed liquor flows upward through the down moving bed of ionexchange particles and maintains the bed in the conventional fluidizedregime;

3. The target ions are adsorbed onto the ion exchange particles when theion exchange particles and the feed contact counter-currently in theparticulate bed;

4. The de-ionized liquid is discarded from the raffinate outlet and theloaded ion exchange particles fall into the bottom wash section;

5. The rinsed ion exchange particles are continuously transported to thesecond fluidized bed through the bottom solids return pipe;

6. Extracting buffer is fed into the base of the second fluidized bedand flows upward at a velocity higher than the terminal velocity of theparticles, thereby maintained in a circulating fluidization regime;

7. The loaded particles are desorbed and regenerated while beingentrained up continuously along the second fluidized bed;

8. The regenerated particles are separated from the extract in theliquid-solids separator at the top; the extract is collected from theextract outlet on the liquid-solid separator and the regeneratedparticles are rinsed in a wash section below the separator;

9. The rinsed particles are fed to the first fluidized bed by gravity.Another cycle begins.

Having described the invention, modifications will be evident to thoseskilled in the art without departing from the spirit of the invention asdefined in the appended claims.

What is claimed is:
 1. A liquid-solid circulating fluidized bed systemcomprising a first liquid fluidized bed, means to feed solids into saidfirst fluidized bed adjacent to a first end of said first fluidized bedand means to feed a first fluid into said first fluidized bed adjacentto a second end of said first fluidized bed, said second end beingremote from said first end so that said solids and said first fluid flowin counter current, a second liquid fluidized bed, said second liquidfluidized bed being an entraining liquid fluidized bed wherein a meansfor introducing solids and a means for introducing a second fluid intosaid second bed are both adjacent to one end of said second fluidizedbed so that said solids and said second fluid introduced into saidsecond bed flow concurrently through said second bed from said one endtoward another end of said second fluidized bed remote from said oneend, first means connecting said first fluidized bed to said secondfluidized bed adjacent to said second end of said first fluidized bedand said one end of said second fluidized bed, said first connectingmeans includes means to feed said solids into said second fluidized bed,second means connecting said first and said second fluidized bedsadjacent said first end of said first bed and said other end of saidsecond fluidized bed, said first means connecting includes means forminga packed moving bed dynamic seal between said first and second fluidizedbeds and said second means connecting includes said means to feed solidsinto said first fluidized bed.
 2. A liquid-solid circulating fluidizedbed sin as defined in claim 1 wherein said first and second liquidfluidized beds are substantially vertical columns.
 3. A liquid-solidcirculating fluidized bed system as defined in claim 2 wherein saidfirst end of said first fluidized bed is the top end, said second end ofsaid first fluidized bed is the bottom end, said one end of the secondfluidized bed is the bottom end and said other end of said secondfluidized bed is the top end.
 4. A liquid-solid circulating fluidizedbed system as defined in claim 3 wherein said first fluid essentiallyflows upwards and said solids essentially flow downwards to form acounter current flow in said first fluidized bed, and wherein saidsecond fluid and solids both essentially flow upwards concurrently inthe second fluidized bed.
 5. A liquid-solid circulating fluidized bedsystem as defined in claim 4 wherein second means connecting said firstand said second liquid fluidized beds includes a washer for washing saidsolids before they are fed into said first end of said first fluidizedbed.
 6. A liquid-solid circulating fluidized bed system as defined inclaim 5 wherein said second means connecting said first and said secondliquid fluidized beds further includes a separator means for separatingsolids from fluid and exhausting such separated fluid to provideseparated solids.
 7. A liquid-solid circulating fluidized bed system asdefined in claim 4 wherein said first means connecting said first andsaid second liquid fluidized beds includes a second washer for washingsolids adjacent to said second end of said first fluidized before theyare introduced into said second fluidized bed.
 8. A liquid-solidcirculating fluidized bed system as defined in claim 4 wherein secondmeans connecting said first and said second liquid fluidized bedsincludes a washer for washing said solids before they are fed into saidfirst end of said first fluidized bed, and a separator means forseparating solids from fluid and exhausting such separated fluid toprovide separated solids.
 9. A liquid-solid circulating fluidized bedsystem as defined in claim 8 wherein said first means connecting saidfirst and said second liquid fluidized beds includes a second washer forwashing solids adjacent to said second end of said first fluidizedbefore they are introduced into said second fluidized be.
 10. Aliquid-solid circulating fluidized bed system as defined in claim 1wherein second means connecting said first and said second liquidfluidized beds includes a washer for washing said solids before they arefed into said first end of said first fluidized bed, and a separatormeans for separating solids from fluid and exhausting such separatedfluid to provide separated solids.
 11. A liquid-solid circulatingfluidized bed system as defined in claim 10 wherein said first meansconnecting said first and said liquid second fluidized beds includes asecond washer for washing solids adjacent to said second end of saidfirst fluidized before they are introduced into said second fluidizedbed.